Method for controlling airflow

ABSTRACT

An airflow control device comprises a body and an active material in operative communication with the body. The active material, such as shape memory material, is operative to change at least one attribute in response to an activation signal. The active material can change its shape, dimensions and/or stiffness producing a change in at least one feature of the airflow control device such as shape, dimension, location, orientation, and/or stiffness to control vehicle airflow to better suit changes in driving conditions such as weather, ground clearance and speed, while reducing maintenance and the level of failure modes. As such, the device reduces vehicle damage due to inadequate ground clearance, while increasing vehicle stability and fuel economy. An activation device, controller and sensors may be employed to further control the change in at least one feature of the airflow control device such as shape, dimension, location, orientation, and/or stiffness of the device. A method for controlling vehicle airflow selectively introduces an activation signal to initiate a change of at least one feature of the device that can be reversed upon discontinuation of the activation signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Division Application of U.S. application Ser. No. 10/893,119,filed Jul. 15, 2004 now U.S. Pat. No. 6,979,050, which relates to, andclaims priority to, U.S. Provisional Application Ser. No. 60/526,785,filed on Dec. 4, 2003, incorporated herein in its entirety.

BACKGROUND

The present disclosure relates to devices for controlling vehicleairflow and, more particularly, to devices for controlling vehicleairflow which can be adjusted through changes in active materials inresponse to varying conditions, the adjustment being affected throughshape, dimension, and/or stiffness changes in the active material.

Airflow over, under, around, and/or through a vehicle can affect manyaspects of vehicle performance including vehicle drag, vehicle lift anddown force, and cooling/heat exchange for a vehicle powertrain and airconditioning systems. Reductions in vehicle drag improve fuel economy.Vehicle lift and downforce can affect vehicle stability and handling. Asused herein, the term “airflow” refers to the motion of air around andthrough parts of a vehicle relative to either the exterior surface ofthe vehicle or surfaces of elements of the vehicle along which exteriorairflow can be directed such as surfaces in the engine compartment. Theterm “drag” refers to the resistance caused by friction in a directionopposite that of the motion of the center of gravity for a moving bodyin a fluid. The term “lift” as used herein refers to the component ofthe total force due to airflow relative to a vehicle acting on thevehicle in a vertically upwards direction. The term “downforce” usedherein refers to the component of total force due to airflow relative tothe vehicle acting on a vehicle in a vertically downward direction.

Devices known in the art of vehicle manufacture to control airflowrelative to a vehicle are generally of a predetermined, non-adjustablegeometry, location, orientation and stiffness. Such devices generally donot adapt as driving conditions change, thus the airflow relative to thevehicle cannot be adjusted to better suit the changing drivingconditions. Additionally, current under-vehicle airflow control devicescan reduce ground clearance. Vehicle designers are faced with thechallenge of controlling the airflow while maintaining sufficient groundclearance to avoid contact with and damage by parking ramps, parkingblocks, potholes, curbs and the like. Further, inclement weather, suchas deep snow slush or rainfall, can damage the device and/or impairvehicle handing.

Current stationary airflow control devices may be adjustable by mountingand/or connecting the devices to hydraulic, mechanical, electricalactuators and/or the like. For example, some vehicle spoilers may adjustlocation and/or orientation in response to an actuator signal. However,such actuators generally require additional components such as pistons,motors, solenoids and/or like mechanisms for activation, which increasethe complexity of the device often resulting in increased failure modes,maintenance, and manufacturing costs. Therefore, there exists a need foran adjustable device for controlling vehicle airflow under varyingdriving conditions that enhances device simplicity while reducing deviceproblems and the number of failure modes.

BRIEF SUMMARY

Disclosed herein is an airflow control device for a vehicle, i.e. airdeflector. The air deflector comprises a body portion having at leastone surface, and an active material in operative communication with theat least one surface, the active material being operative to change atleast one attribute in response to an activation signal, wherein anairflow across the air deflector changes with the change in the at leastone attribute of the active material.

Also disclosed is a system for controlling vehicle airflow comprising astationary surface of a vehicle; and an air deflector fixedly attachedto the stationary surface, the air deflector comprising an airdeflecting body having at least one surface, an active material inoperative communication with the at least one surface, the activematerial being operative to change a feature of the deflecting body inresponse to an activation signal, and an activation device in functionalcommunication with the active material, the activation device beingoperable to selectively provide the activation signal, the activationsignal initiates a change in at least one attribute of the activematerial, wherein the change in at least one attribute of the activematerial changes a feature of the air deflecting body.

A method for controlling vehicle airflow is also disclosed positioningan airflow controlling device on a stationary surface of the vehicle,the airflow controlling device comprising a body having at least onesurface, and an active material in operative communication with the atleast one surface, the active material being operative to change a atleast one attribute in response to an activation signal; selectivelyintroducing the activation signal upon meeting and/or exceeding apredetermined vehicle condition; and changing the at least one attributeof the active material from a first at least one attribute to a secondat least one attribute.

The above described and other features are exemplified by the followingfigures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are meant to be exemplaryembodiments, and wherein the like elements are numbered alike:

FIG. 1 is a perspective view of an airflow control device in accordancewith the present disclosure;

FIGS. 2 a and 2 b are perspective views of an airflow control devicehaving an active material on a surface in accordance with the presentdisclosure;

FIG. 3 a is a perspective view of an airflow control device havingactive material embedded within a surface of the body in accordance withan embodiment of the present disclosure;

FIG. 3 b is a perspective view of an airflow device having activematerial embedded within the body in accordance with an embodiment ofthe present disclosure; and

FIG. 4 is a perspective view of an airflow control device wherein anactive material is connected externally to the surface of the airflowcontrol device in accordance with an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

The present disclosure provides an airflow control device for a vehicle,wherein the airflow control device is capable of reversibly changingshape, dimension, orientation, location and/or stiffness, the changebeing effected through the activation of an active material, allowingthe airflow control device to adapt to varying driving conditions.Employing the active materials as described herein advantageouslyprovides an actuation mechanism that is lightweight, inherently robust,and lower in complexity than prior external actuation means. Moreover,the airflow control devices described herein are also of low cost and ofeasily adaptable design that may be integrated with limited changes tothe existing structure. As used herein the term “vehicles” includes anystructure subject to airflow including, but not intended to be limitedto, automobiles, over the highway tractors, boats, motorcycles,airplanes, bobsleds, spaceship, and the like.

As shown in FIG. 1, an airflow control device for a vehicle (alsoreferred to herein as an air deflector), generally indicated asreference numeral 10, comprises a body portion 12 having at least onesurface 13, 14, 15 and an active material 16 in operative communicationwith at least one surface 13, 14, 15 and/or the body 12, the activematerial 16 having a first at least one attribute that is operative tochange in response to an activation signal to the active material 16. Anattribute of the active material 16, and changes thereof, refer tocharacteristics of the active material 16 such as, but not limited to,shape, dimension, stiffness, combinations thereof, and the like. Thechanges in at least one attribute of the active material 16 affectvarious features of the airflow device 10 such as, but not limited to,shape, dimension, location, orientation, stiffness, combinationsthereof, and/or the like, resulting in a change in the airflow acrossthe device 10. In this manner, the device 10 is adjustable and airflowacross the device 10 changes with the change in at least one attributeof the active material 16 under varying driving conditions.

Using an automobile as an example, the airflow control device 10 may beof any of a variety of configurations, including but not limited to, airdams; fender flares; side skirt cribs; cabs; rear and tailgate spoilers;louvers for controlling airflow through radiator, other heat exchangers,the engine compartment, over the drive train and transmission; and airand wind deflectors for roof tops, sunroofs, vent windows; and likeconfigurations. An exemplary air dam comprises a projection of the bodyshell underneath the front of the chassis of a vehicle and functions toreduce the amount of air turbulence and drag underneath the vehicle, aswell as channels cooling air to the radiator. Further, many airflowcontrol devices, and air deflectors in particular, improve vehiclestability and increase gas mileage. For example, at low speeds the airdam can be actively positioned so that additional ground clearance isprovided, such as may be desired to clear speed bumps, provide curbclearance for parking, and the like. At higher speeds, the air dam canbe actively positioned to divert the incoming airflow into the coolingsystem, or divert air about the vehicle to improve aerodynamics, improvevehicle stability, increase gas mileage, and the like. It will beunderstood that the device 10 may be a portion of a vehicle louversystem and/or an independent component of the vehicle.

The body 12 (also referred to herein as an air deflecting body) may beany of a variety of materials and configurations that enable the airflowdevice 10 to function, and may further comprise at least one surface 13,14, or 15. In one embodiment, the body 12 is comprised of a flexiblematerial that exhibits adequate flexibility to operate as an adjustableairflow control device as the active material 16 changes at least oneattribute. In an additional embodiment, the body 12 may comprise one ormore active material 16. The active material 16 may change at least oneattribute in response to an activation signal, and revert back to theoriginal state of the at least one attribute upon discontinuation of theactivation signal, or, for the classes of active materials that do notautomatically revert upon discontinuation of the activation signal,alternative means can be employed to revert the active materials totheir original state as will be discussed in detail herein. In thismanner, the airflow control device 10 functions to adjust to changingdriving conditions while increasing device simplicity and reducing thenumber of failure modes.

Active material 16 includes those compositions that can exhibit a changein stiffness properties, shape and/or dimensions in response to theactivation signal, which can take the type for different activematerials 16, of electrical, magnetic, thermal and like fields.Preferred active materials 16 include but are not limited to the classof shape memory materials, and combinations thereof. Shape memorymaterials generally refer to materials or compositions that have theability to remember their original at least one attribute such as shape,which can subsequently be recalled by applying an external stimulus, aswill be discussed in detail herein. As such, deformation from theoriginal shape is a temporary condition. In this manner, shape memorymaterials can change to the trained shape in response to an activationsignal. Exemplary active materials include shape memory alloys (SMA),shape memory polymers (SMP), electroactive polymers (EAP), ferromagneticSMAs, electrorheological fluids (ER), magnetorheological fluids (MR),dielectric elastomers, ionic polymer metal composites (IPMC),piezoelectric polymers, piezoelectric ceramics, various combinations ofthe foregoing materials, and the like.

Shape memory alloys (SMA's) generally refer to a group of metallicmaterials that demonstrate the ability to return to some previouslydefined shape or size when subjected to an appropriate thermal stimulus.Shape memory alloys are capable of undergoing phase transitions in whichtheir yield strength, stiffness, dimension and/or shape are altered as afunction of temperature. The term “yield strength” refers to the stressat which a material exhibits a specified deviation from proportionalityof stress and strain. Generally, in the low temperature, or martensitephase, shape memory alloys can be plastically deformed and upon exposureto some higher temperature will transform to an austenite phase, orparent phase, returning to their shape prior to the deformation.Materials that exhibit this shape memory effect only upon heating arereferred to as having one-way shape memory. Those materials that alsoexhibit shape memory upon re-cooling are referred to as having two-wayshape memory behavior.

Suitable shape memory alloy materials include, without limitation,nickel-titanium based alloys, indium-titanium based alloys,nickel-aluminum based alloys, nickel-gallium based alloys, copper basedalloys (e.g., copper-zinc alloys, copper-aluminum alloys, copper-gold,and copper-tin alloys), gold-cadmium based alloys, silver-cadmium basedalloys, indium-cadmium based alloys, manganese-copper based alloys,iron-platinum based alloys, iron-platinum based alloys, iron-palladiumbased alloys, and the like. The alloys can be binary, ternary, or anyhigher order so long as the alloy composition exhibits a shape memoryeffect, e.g., change in shape orientation, damping capacity, and thelike. For example, a nickel-titanium based alloy is commerciallyavailable under the trademark NITINOL from Shape Memory Applications,Inc.

Shape memory polymers (SMP's) are known in the art and generally referto a group of polymeric materials that demonstrate the ability to returnto some previously defined shape when subjected to an appropriatethermal stimulus. Shape memory polymers are capable of undergoing phasetransitions in which their shape is altered as a function oftemperature. Generally, SMP's have two main segments, a hard segment anda soft segment. The previously defined or permanent shape can be set bymelting or processing the polymer at a temperature higher than thehighest thermal transition followed by cooling below that thermaltransition temperature. The highest thermal transition is usually theglass transition temperature (Tg) or melting point of the hard segment.A temporary shape can be set by heating the material to a temperaturehigher than the Tg or the transition temperature of the soft segment,but lower than the Tg or melting point of the hard segment. Thetemporary shape is set while processing the material at the transitiontemperature of the soft segment followed by cooling to fix the shape.The material can be reverted back to the permanent shape by heating thematerial above the transition temperature of the soft segment.

Suitable shape memory polymers include thermoplastics, thermosets,interpenetrating networks, semi-interpenetrating networks, or mixednetworks. The polymers can be a single polymer or a blend of polymers.The polymers can be linear or branched thermoplastic elastomers withside chains or dendritic structural elements. Suitable polymercomponents to form a shape memory polymer include, but are not limitedto, polyphosphazenes, poly(vinyl alcohols), polyamides, polyesteramides, poly(amino acid)s, polyanhydrides, polycarbonates,polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols,polyalkylene oxides, polyalkylene terephthalates, polyortho esters,polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyesters,polylactides, polyglycolides, polysiloxanes, polyurethanes, polyethers,polyether amides, polyether esters, and copolymers thereof. Examples ofsuitable polyacrylates include poly(methyl methacrylate), poly(ethylmethacrylate), ply(butyl methacrylate), poly(isobutyl methacrylate),poly(hexyl methacrylate), poly(isodecyl methacrylate), poly(laurylmethacrylate), poly(phenyl methacrylate), poly(methyl acrylate),poly(isopropyl acrylate), poly(isobutyl acrylate) and poly(octadecylacrylate). Examples of other suitable polymers include polystyrene,polypropylene, polyvinyl phenol, polyvinylpyrrolidone, chlorinatedpolybutylene, poly(octadecyl vinyl ether) ethylene vinyl acetate,polyethylene, poly(ethylene oxide)-poly(ethylene terephthalate),polyethylene/nylon (graft copolymer), polycaprolactones-polyamide (blockcopolymer), poly(caprolactone) dimethacrylate-n-butyl acrylate,poly(norbornyl-polyhedral oligomeric silsequioxane), polyvinylchloride,urethane/butadiene copolymers, polyurethane block copolymers,styrene-butadiene-styrene block copolymers, and the like.

The active material 16 may also comprise an electroactive polymer suchas ionic polymer metal composites, conductive polymers, piezoelectricmaterial and the like. As used herein, the term “piezoelectric” is usedto describe a material that mechanically deforms when a voltagepotential is applied, or conversely, generates an electrical charge whenmechanically deformed.

Suitable MR elastomer materials include, but are not intended to belimited to, an elastic polymer matrix comprising a suspension offerromagnetic or paramagnetic particles, wherein the particles aredescribed above. Suitable polymer matrices include, but are not limitedto, poly-alpha-olefins, natural rubber, silicone, polybutadiene,polyethylene, polyisoprene, and the like.

Electroactive polymers include those polymeric materials that exhibitpiezoelectric, pyroelectric, or electrostrictive properties in responseto electrical or mechanical fields. The materials generally employ theuse of compliant electrodes that enable polymer films to expand orcontract in the in-plane directions in response to applied electricfields or mechanical stresses. An example of an electrostrictive-graftedelastomer with a piezoelectric poly(vinylidenefluoride-trifluoro-ethylene) copolymer. This combination has the abilityto produce a varied amount of ferroelectric-electrostrictive molecularcomposite systems. These may be operated as a piezoelectric sensor oreven an electrostrictive actuator.

Materials suitable for use as an electroactive polymer may include anysubstantially insulating polymer or rubber (or combination thereof) thatdeforms in response to an electrostatic force or whose deformationresults in a change in electric field. Exemplary materials suitable foruse as a pre-strained polymer include silicone elastomers, acrylicelastomers, polyurethanes, thermoplastic elastomers, copolymerscomprising PVDF, pressure-sensitive adhesives, fluoroelastomers,polymers comprising silicone and acrylic moieties, and the like.Polymers comprising silicone and acrylic moieties may include copolymerscomprising silicone and acrylic moieties, polymer blends comprising asilicone elastomer and an acrylic elastomer, for example.

Materials used as an electroactive polymer may be selected based on oneor more material properties such as a high electrical breakdownstrength, a low modulus of elasticity (for large or small deformations),a high dielectric constant, and the like. In one embodiment, the polymeris selected such that is has an elastic modulus at most about 100 MPa.In another embodiment, the polymer is selected such that is has amaximum actuation pressure between about 0.05 MPa and about 10 MPa, andpreferably between about 0.3 MPa and about 3 MPa. In another embodiment,the polymer is selected such that is has a dielectric constant betweenabout 2 and about 20, and preferably between about 2.5 and about 12. Thepresent disclosure is not intended to be limited to these ranges.Ideally, materials with a higher dielectric constant than the rangesgiven above would be desirable if the materials had both a highdielectric constant and a high dielectric strength. In many cases,electroactive polymers may be fabricated and implemented as thin films.Thicknesses suitable for these thin films may be below 50 micrometers.

As electroactive polymers may deflect at high strains, electrodesattached to the polymers should also deflect without compromisingmechanical or electrical performance. Generally, electrodes suitable foruse may be of any shape and material provided that they are able tosupply a suitable voltage to, or receive a suitable voltage from, anelectroactive polymer. The voltage may be either constant or varyingover time. In one embodiment, the electrodes adhere to a surface of thepolymer. Electrodes adhering to the polymer are preferably compliant andconform to the changing shape of the polymer. Correspondingly, thepresent disclosure may include compliant electrodes that conform to theshape of an electroactive polymer to which they are attached. Theelectrodes may be only applied to a portion of an electroactive polymerand define an active area according to their geometry. Various types ofelectrodes suitable for use with the present disclosure includestructured electrodes comprising metal traces and charge distributionlayers, textured electrodes comprising varying out of plane dimensions,conductive greases such as carbon greases or silver greases, colloidalsuspensions, high aspect ratio conductive materials such as carbonfibrils and carbon nanotubes, and mixtures of ionically conductivematerials.

Materials used for electrodes of the present disclosure may vary.Suitable materials used in an electrode may include graphite, carbonblack, colloidal suspensions, thin metals including silver and gold,silver filled and carbon filled gels and polymers, and ionically orelectronically conductive polymers. It is understood that certainelectrode materials may work well with particular polymers and may notwork as well for others. By way of example, carbon fibrils work wellwith acrylic elastomer polymers while not as well with siliconepolymers.

The active material may also comprise a piezoelectric material. Also, incertain embodiments, the piezoelectric material may be configured as anactuator for providing rapid deployment. As used herein, the term“piezoelectric” is used to describe a material that mechanically deforms(changes shape) when a voltage potential is applied, or conversely,generates an electrical charge when mechanically deformed. Preferably, apiezoelectric material is disposed on strips of a flexible metal orceramic sheet. The strips can be unimorph or bimorph. Preferably, thestrips are bimorph, because bimorphs generally exhibit more displacementthan unimorphs.

One type of unimorph is a structure composed of a single piezoelectricelement externally bonded to a flexible metal foil or strip, which isstimulated by the piezoelectric element when activated with a changingvoltage and results in an axial buckling or deflection as it opposes themovement of the piezoelectric element. The actuator movement for aunimorph can be by contraction or expansion. Unimorphs can exhibit astrain of as high as about 10%, but generally can only sustain low loadsrelative to the overall dimensions of the unimorph structure. Acommercial example of a pre-stressed unimorph is referred to as“THUNDER”, which is an acronym for THin layer composite UNimorphferroelectric Driver and sEnsoR. THUNDER is a composite structureconstructed with a piezoelectric ceramic layer (for example, leadzirconate titanate), which is electroplated on its two major faces. Ametal pre-stress layer is adhered to the electroplated surface on atleast one side of the ceramic layer by an adhesive layer (for example,“LaRC-SI®” developed by the National Aeronautics and SpaceAdministration (NASA)). During manufacture of a THUNDER actuator, theceramic layer, the adhesive layer, and the first pre-stress layer aresimultaneously heated to a temperature above the melting point of theadhesive, and then subsequently allowed to cool, thereby re-solidifyingand setting the adhesive layer. During the cooling process the ceramiclayer becomes strained, due to the higher coefficients of thermalcontraction of the metal pre-stress layer and the adhesive layer than ofthe ceramic layer. Also, due to the greater thermal contraction of thelaminate materials than the ceramic layer, the ceramic layer deformsinto an arcuate shape having a generally concave face.

In contrast to the unimorph piezoelectric device, a bimorph deviceincludes an intermediate flexible metal foil sandwiched between twopiezoelectric elements. Bimorphs exhibit more displacement thanunimorphs because under the applied voltage one ceramic element willcontract while the other expands. Bimorphs can exhibit strains up toabout 20%, but similar to unimorphs, generally cannot sustain high loadsrelative to the overall dimensions of the unimorph structure.

Suitable piezoelectric materials include inorganic compounds, organiccompounds, and metals. With regard to organic materials, all of thepolymeric materials with non-centrosymmetric structure and large dipolemoment group(s) on the main chain or on the side-chain, or on bothchains within the molecules, can be used as candidates for thepiezoelectric film. Examples of suitable polymers include, for example,but are not limited to, poly(sodium 4-styrenesulfonate) (“PSS”), polyS-119 (poly(vinylamine)backbone azo chromophore), and their derivatives;polyfluorocarbons, including polyvinylidene fluoride (“PVDF”), itsco-polymer vinylidene fluoride (“VDF”), trifluoroethylene (TrFE), andtheir derivatives; polychlorocarbons, including poly(vinyl chloride)(“PVC”), polyvinylidene chloride (“PVC2”), and their derivatives;polyacrylonitriles (“PAN”), and their derivatives; polycarboxylic acids,including poly(methacrylic acid (“PMA”), and their derivatives;polyureas, and their derivatives; polyurethanes (“PUE”), and theirderivatives; bio-polymer molecules such as poly-L-lactic acids and theirderivatives, and membrane proteins, as well as phosphate bio-molecules;polyanilines and their derivatives, and all of the derivatives oftetramines; polyimides, including Kapton molecules and polyetherimide(“PEI”), and their derivatives; all of the membrane polymers;poly(N-vinyl pyrrolidone) (“PVP”) homopolymer, and its derivatives, andrandom PVP-co-vinyl acetate (“PVAc”) copolymers; and all of the aromaticpolymers with dipole moment groups in the main-chain or side-chains, orin both the main-chain and the side-chains, and mixtures thereof.

Further, piezoelectric materials can include Pt, Pd, Ni, Ti, Cr, Fe, Ag,Au, Cu, and metal alloys and mixtures thereof. These piezoelectricmaterials can also include, for example, metal oxide such as SiO2,Al2O3, ZrO2, TiO2, SrTiO3, PbTiO3, BaTiO3, FeO3, Fe3O4, ZnO, andmixtures thereof; and Group VIA and IIB compounds, such as CdSe, CdS,GaAs, AgCaSe 2, ZnSe, GaP, InP, ZnS, and mixtures thereof.

Suitable active materials also comprise magnetorheological (MR)compositions, such as MR elastomers, which are known as “smart”materials whose rheological properties can rapidly change uponapplication of a magnetic field. MR elastomers are suspensions ofmicrometer-sized, magnetically polarizable particles in a thermosetelastic polymer or rubber. The stiffness of the elastomer structure isaccomplished by changing the shear and compression/tension moduli byvarying the strength of the applied magnetic field. The MR elastomerstypically develop structure when exposed to a magnetic field in aslittle as a few milliseconds. Discontinuing the exposure of the MRelastomers to the magnetic field reverses the process and the elastomerreturns to its lower modulus state.

The airflow control device 10, illustrated in FIG. 1, may comprise oneor more of the above noted active materials 16 applied as a coating, alayer, and/or sections such as strips to at least one surface 13, 14,and/or 15 of the body 12. In one embodiment, different active materialsare applied to a surface 13, 14, 15, wherein the different activematerials 16 are applied adjacent to one another. In another embodiment,the active material 16 may comprise a composite of different shapememory materials. In either embodiment, the active material 16 providesthe airflow device 10 with a shape changing capability that can beactively-tuned to a particular application, as will be described ingreater detail.

Coupled to and in operative communication with airflow device 10 is anactivation device 18. The activation device 18 is in functionalcommunication with the airflow device 10 and/or active material 16,which is operable to selectively provide an activation signal to theairflow control device 10 and change a feature of the airflow device 10by changing at least one attribute of the active material 16. Forexample, in the case of an underflow airflow device, the active material16 can retract or extend the airflow device 10 depending on the speed ofthe vehicle. The activation device 18, on demand, provides theactivation signal or stimulus to the active material 16 of the airflowdevice 10 to cause the change in one or more feature of at least aportion of the device 10. In one embodiment, the change in featuregenerally remains for the duration of the applied activation signal.Upon discontinuation of the activation signal, the active material 16generally reverts to an unpowered form and returns substantially to theoriginal at least one attribute, thus reverting the airflow device 10 tothe original feature and/or features. In another embodiment, the changein one or more attributes of the active material 16 and/or feature of atleast a portion of the device 10 may remain upon discontinuing theactivation signal. In this embodiment, the device 10 includes a means tomaintain the change in active material 16, such as a latch 28, lock,stop and/or the like. Upon release of the means, the device 10 revertsback to the original at least one feature. The illustrated device 10 isexemplary only and is not intended to be limited to any particularshape, size, dimension or configuration, material, or the like.

In another embodiment, the airflow device 10 includes at least onesensor 26 in operative communication with the airflow control device 10and/or the active material 16, wherein the sensor is adapted to transmitsignals indicative of at least one vehicle condition. This embodimentmay further comprise a controller 24 that is operatively connected tothe sensor 26 and activation device 18, wherein the controller isprogrammed and configured to cause the activation device 18 to providean activation signal to the active material 16 when the sensor 26signals indicate a predetermined vehicle condition.

The present disclosure is not intended to be limited to any particularactivation signal. The particular activation signal will depend on thesensitivity of the active material 16. As such, the activation signalmay provide a thermal activation signal, magnetic activation signal,electrical activation signal, chemical activation signal, and/or otherlike activation signal or combination of activation signals.

As shown in FIGS. 2 a and 2 b, perspective views of an airflow controldevice designated as reference numeral 200 may comprise a body 212having one or more surfaces 213, 214, and 215 to control airflow. In oneembodiment, the body 212 of the airflow device 200 is formed of activematerial 216. In another embodiment, the body 212 may be formed entirelyof the active material 216 or other suitable compositions having one ormore surfaces 213, 214, 215 comprising one or more active materials 216.The active materials 216 in this device 200 as shown in FIG. 2 a, mayhave a substantially straight shape at room temperature and, as shown inFIG. 2 b, a curved shape (i.e. curvilinear shape) when heated above atemperature range that may be generally encountered during vehicleoperation. In this view, the airflow device 200 may control airflow suchas is provided in the direction indicated by arrow 230 while maintainingsufficient ground clearance to avoid contact with and damage by roadhazards and inclement weather residue. In this embodiment, the activematerial is preferably selected to be sensitive to thermal activation.The linear shape shown in FIG. 2 a is effective for preventing the flowof air whereas the curvilinear shape as shown in FIG. 2 b provided byactivation of the active material 216 can provide increased airflowrelative to the linear shape.

As shown, one or more wires 222 are embedded in the active material 216of the device 200 to provide a thermal activation means in the form ofresistive heating. The wires 222 are shown in the form of a mesh likescreen to facilitate uniform heating of the body 212, which is formed ofthermally active material 216, e.g., shape memory polymer. Although amesh like form is shown, one of skill in the art will appreciate thatother variations can be used such as wires, films, and the like, theconfigurations of which are well known and within the skill of those inthe art of resistive heating. The wires heat up when an electric currentpasses through them due to electrical resistance, which is transferreddirectly to the thermally active material to effect a change in at leastone attribute thereof. In additional embodiments, controls such ascontroller 224 and/or sensor 226 may cause a current to flow through theembedded wires 222 at low driving speed causing the active material 216to curve upward, assuming a trained higher temperature shape. This mayresult in a rise in the airflow control device 200 and in doing soincrease vehicle ground clearance. Further, when driving above apredetermined speed, the controller 224 may discontinue the current andallow the airflow control device 200 to cool, and thus straighten anddeploy. In another embodiment, the change in feature may be reversedsuch that at higher vehicle speed heating may be employed to achieve ahigh temperature shape, and current would be discontinued at lowervehicle speed to achieve a low temperature shape. In another embodiment,the change in one or more attribute of the active material 216 and/orfeature of the device 200 may remain upon discontinuing the activationsignal. In this embodiment, the device 200 includes a means to maintainthe change in active material 216 such as a latch 228, lock stop and/orthe like. Upon release of the means to maintain the change in activematerial 216, the device 200 reverts back to the original at least onefeature. In this manner, the device 200 may curve upward in response tothe activation signal, maintain the upward curve until release of themeans, where upon the device 200 will revert and straighten. Further,the airflow control device 200 can be restored and healed to a desiredshape by heating the active material 216 to the appropriate temperature.In this manner, an airflow control device 200 that becomes deformed,such as during an impact, may be restored or healed to a desired shapeby applying the appropriate temperature range. The selection of materialcomprising the body 212 and/or active material 216 will be determined bythe desired application. Moreover, selection of then locking means iswell within the skill of those in the art.

As shown in FIGS. 3 a and 3 b, perspective views of an airflow controldevice designated as reference numeral 300, are shown, having stripsand/or sections formed of active material 316. In FIG. 3 a, the device300 comprises strips and/or sections of active material 316 embedded onsurface 314 of the body 312. However, it should be noted that the activematerial 316 could be embedded in any one or more of the surfaces 313,314, and 315 that define the airflow control device 300. In an alternateembodiment shown in FIG. 3B, the strips and/or sections of activematerial 313 are embedded within the body 312 as shown in the device300′. In these embodiments, the body 312 comprises a flexible matrixmaterial with strips of active material 316, preferably but notnecessarily, embedded at regular intervals. The placement of the activematerial 316 is not limited to any particular configuration or patternand will be determined by the desired application of the device 300,300′. In one embodiment, as in strips of SMA, the active material 316has a trained curved shape in the austenite phase, not shown in thisview. At standing or low vehicle speeds, the active material 316 may beheated through resistance heating which may cause the active material316 to change its shape to a curvilinear shave and in doing so curl theairflow control device 300 or 300′ up and out of the external airflowsuch as may be provided in the direction indicated by arrow 330. Thechange in shape may be initiated by an activation signal transmitted byactivation device 318, controller 324, and/or sensor 326. For example,as previously discussed the activation device 318 can provide anelectrical signal, e.g., a current, to resistively heat the shape memoryalloy wires as shown in FIG. 3A. One of skill in the art would know thatto resistively heat a wire such as the shape memory alloy disclosedherein, one simply flows a current I from a power source 332 through acircuit 331 that includes the shape memory alloy 316. The shape memoryalloy strips 316 can be in series, in parallel, or individually coupledto the circuit. The current I flowing through the circuit 331 willresistively heat the shape memory alloy as a function of the resistanceprovided by the shape memory alloy 316.

With regard to SMAs, as a result of the change in phase, the stiffnessin the austenite phase will be greater than the stiffness in themartensite phase. The number and size of the embedded active materialstrips may be chosen such that when in the austenite phase the embeddedactive material 316 causes the bulk of the airflow control device 300 todeform. However, when the active material 316 is in the martensitephase, the flexible material comprising the bulk of the airflow controldevice 300, 300′ is sufficiently stiff to return the device 300 to astraight, deployed configuration, and in doing so straightening theactive material 316. At higher speeds, in excess of a predeterminedvehicle speed, the current flow causing resistant heating may bestopped, causing the active material 316 to return to the martensitephase. In this manner, the airflow control device 300, 300′ reverts to astraightened deployed state. As previously discussed, the airflowcontrol device 300, 300′ may be restored if deformed as a result offorce, such as an impact, due to plastic deformation of the strips ofactive material 316 by heating the active material 316 to the austenitephase temperature. The other materials noted above can be activated in asimilar manner using a suitable activation signal particular to theselected active material as will be appreciated by those skilled in theart in view of this disclosure.

In an additional embodiment, shown in FIG. 4, a perspective view of anairflow control device 400 comprises active material 416 in the shape ofhelical springs positioned in functional operation to the body 412 ofthe airflow control device 400. In this embodiment, the active material416 may be connected externally either directly or remotely to aselected surface 413, 414, 415 defining the body 412 of the airflowcontrol device 400. As shown in FIG. 4, a surface 413 of the body 412 iscoupled with a hollow tube 442 in such a fashion that the hollow tube420 is free to rotate about its axis. A biased spring mechanism 442 andthe active material 416 are both coupled to the hollow tube 420 in anopposing fashion such that their respective tensions balance each other.In this manner, the rotation of the hollow tube 442 through externalmeans may increase the tension in one direction while reducing tensionin the other direction. At low vehicle speeds (i.e., less than apredetermined speed), tension in the spring mechanism 444 combined withreduced stiffness and greater length of an unheated active material 416results in rotation of the airflow control device 400 out of the airflowsuch as may be provided in the direction indicated by arrow 430. Athigher speed (i.e., greater than the predetermined speed), thetemperature of the active material 416 can be raised through resistanceheating or conductive heating such as immersion into engine coolant orthe like to produce a phase change in the active material 416 from themartensite phase to the austenite phase. The wires comprised of activematerial 416 preferably exhibit up to about a 4 percent (%) reduction inlength with an up to 3 times increase in stiffness properties. In thismanner, the combined reduction in length and increase in stiffnessproperties can result in deployment of the airflow control device 400,e.g., such as rotation of the tube 442 and stretching of thecounter-balancing spring mechanism 444. Upon discontinuation of theresistance heating, the active material 416 cools to the martensitephase and the stretched spring mechanism 444 can be used to return theairflow control device 400 to a stowed position. In another embodiment,the change in one or more attribute of the active material 416 and/orfeature of the device 400 may remain upon discontinuing the activationsignal. In this embodiment, the device 400 includes a means to maintainthe change in active material 416, such as a latch 428, lock, stop an/orthe like. Upon release of the means to maintain the change in activematerial 416, the device 400 reverts back to the original at least onefeature. As previously discussed, the activation device 418, controller424 and/or sensor 426 may function with each other and the airflowcontrol device 400 to initiate the changes in at least one attribute ofthe active material 416.

A method of controlling vehicle airflow is disclosed. In thisembodiment, the method first comprises positioning the airflowcontrolling device 10, 200, 300, or 400 so as to provide airflow incontact during movement of the vehicle, the airflow controlling devicecomprising a body and an active material in operative communication withthe body, wherein the active material is operative to change at leastone attribute in response to an activation signal. Once positioned, anactivation signal is selectively introduced to the active material e.g.16, 216, 316, 416. By selectively introducing the activation signal, atleast one attribute of the active material changes. In anotherembodiment, the method includes discontinuing the activation signal toreverse the change of at least one attribute of the active material. Inan additional embodiment, the method includes maintaining the change inat least one attribute of the active material upon discontinuation ofthe activation signal.

As previously discussed, suitable shape memory materials that canundergo a shape change in response to an activation signal include shapememory alloy compositions. Shape memory alloys exist in severaldifferent temperature-dependent phases. The most commonly utilized ofthese phases are the so-called martensite and austenite phases discussedabove. In the following discussion, the martensite phase generallyrefers to the more deformable, lower temperature phase whereas theaustenite phase generally refers to the more rigid, higher temperaturephase. When the shape memory alloy is in the martensite phase and isheated, it begins to change into the austenite phase. The temperature atwhich this phenomenon starts is often referred to as austenite starttemperature (As). The temperature at which this phenomenon is completeis called the austenite finish temperature (Af). When the shape memoryalloy is in the austenite phase and is cooled, it begins to change intothe martensite phase, and the temperature at which this phenomenonstarts is referred to as the martensite start temperature (Ms). Thetemperature at which austenite finishes transforming to martensite iscalled the martensite finish temperature (Mf). Generally, the shapememory alloys are softer and more easily deformable in their martensiticphase and are harder, stiffer, and/or more rigid in the austeniticphase. In view of the foregoing, a suitable activation signal for usewith shape memory alloys is a thermal activation signal having amagnitude to cause transformations between the martensite and austenitephases.

Shape memory alloys can exhibit a one-way shape memory effect, anintrinsic two-way effect, or an extrinsic two-way shape memory effectdepending on the alloy composition and processing history. Annealedshape memory alloys typically only exhibit the one-way shape memoryeffect. Sufficient heating subsequent to low-temperature deformation ofthe shape memory material will induce the martensite to austenite typetransition, and the material will recover the original, annealed shape.Hence, one-way shape memory effects are only observed upon heating.Active materials comprising shape memory alloy compositions that exhibitone-way memory effects do not automatically reform, and will likelyrequire an external mechanical force to reform the shape that waspreviously suitable for airflow control.

Intrinsic and extrinsic two-way shape memory materials are characterizedby a shape transition both upon heating from the martensite phase to theaustenite phase, as well as an additional shape transition upon coolingfrom the austenite phase back to the martensite phase. Active materialsthat exhibit an intrinsic shape memory effect are fabricated from ashape memory alloy composition that will cause the active materials toautomatically reform themselves as a result of the above noted phasetransformations. Intrinsic two-way shape memory behavior must be inducedin the shape memory material through processing. Such procedures includeextreme deformation of the material while in the martensite phase,heating-cooling under constraint or load, or surface modification suchas laser annealing, polishing, or shot-peening. Once the material hasbeen trained to exhibit the two-way shape memory effect, the shapechange between the low and high temperature states is generallyreversible and persists through a high number of thermal cycles. Incontrast, active materials that exhibit the extrinsic two-way shapememory effects are composite or multi-component materials that combine ashape memory alloy composition that exhibits a one-way effect withanother element that provides a restoring force to reform the originalshape.

The temperature at which the shape memory alloy remembers its hightemperature form when heated can be adjusted by slight changes in thecomposition of the alloy and through heat treatment. In nickel-titaniumshape memory alloys, for instance, it can be changed from above about100° C. to below about −100° C. The shape recovery process occurs over arange of just a few degrees and the start or finish of thetransformation can be controlled to within a degree or two depending onthe desired application and alloy composition. The mechanical propertiesof the shape memory alloy vary greatly over the temperature rangespanning their transformation, typically providing the airflow controldevices with shape memory effects, superelastic effects, and highdamping capacity.

Another suitable class of shape memory material is SMPs. Most shapememory polymers exhibit a “one-way” effect, wherein the SMP exhibits onepermanent shape. Upon heating the SMP above the first transitiontemperature, the permanent shape is achieved and the shape will notrevert back to the temporary shape without the use of outside forces.For example, for active materials which exhibit differences in stiffnessof the activated and non-activated states, energy may be storedelastically during the activation of the airflow control device 10, 200,300, 400. As such, the energy may be stored in any manner suitable foroperation of the airflow control device 10, 200, 300, 400 including, butnot limited to, within the body (e.g., 12, 212, 312, 412) of the device10, 200, 300, 400 and/or in elastic components such as springs whichoperate internally to and/or externally connected to the device 10, 200,300, 400. In this manner, the stored energy is available to revert thedevice 10, 200, 300, 400 to an original state of at least feature suchas shape, dimension, stiffness, location and/or orientation upondiscontinuation of an activation signal and/or release of a means, suchas a latch, lock, stop and/or the like, as discussed herein. In anotherexample, more than one active materials which exhibit differences instiffness of the activated and non-activated states are oriented so asto oppose the change in at least one attribute each produces. As such,one or more opposing active material may be selectively activatedwithout the activation of other opposing active materials. In thismanner, the change in at least one attribute of the selectivelyactivated active material may be reversed by deactivating the activatedactive materials, and selectively activating other opposing activematerials. Alternatively, the active material can be activated during ano load condition so as to permit reversion to its original shape. Theabove-mentioned examples are illustrative and do not limit theembodiments of the present disclosure.

As an alternative, some shape memory polymer compositions can beprepared having a “two-way” effect. These systems consist of at leasttwo polymer components. For example, one component could be a firstcross-linked polymer while the other component is a differentcross-linked polymer. The components are combined by layer techniques,or are interpenetrating networks, wherein two components arecross-linked but not to each other. By changing the temperature, theshape memory polymer changes its shape in the direction of the firstpermanent shape or the second permanent shape. Each of the permanentshapes belongs to one component of the shape memory polymer. The twopermanent shapes are always in equilibrium between both shapes. Thetemperature dependence of the shape is caused by the fact that themechanical properties of one component (“component A”) are almostindependent from the temperature in the temperature interval ofinterest. The mechanical properties of the other component (“componentB”) depend on the temperature. In one embodiment, component B becomesstronger at low temperatures compared to component A, while component Ais stronger at high temperatures and determines the actual shape. Atwo-way memory device can be prepared by setting the permanent shape ofcomponent A (“first permanent shape”); deforming the device into thepermanent shape of component B (“second permanent shape”); and fixingthe permanent shape of component B while applying a stress to thecomponent.

In a preferred embodiment, the permanent shape of the active materiale.g. 16, 216, 316, 416 is a substantially straightened shape and thetemporary shape of the active material is a curved shape (see, forexample, FIGS. 2 a and 2 b). In another embodiment, the shape memorypolymer comprises two permanent shapes. In the first permanent shape theactive materials are in a substantially straightened shape and in thesecond permanent shape, the active materials are in a curved shape.

The temperature needed for permanent shape recovery can be set at anytemperature between about −63° C. and about 120° C. or above.Engineering the composition and structure of the polymer itself canallow for the choice of a particular temperature for a desiredapplication. A preferred temperature for shape recovery is greater thanor equal to about −30° C., more preferably greater than or equal toabout 0° C., and most preferably a temperature greater than or equal toabout 50° C. Also, a preferred temperature for shape recovery is lessthan or equal to about 120° C., and most preferably less than or equalto about 120° C. and greater than or equal to about 80° C.

As previously mentioned and defined, the active material 16 may alsocomprise an electroactive polymer such as ionic polymer metalcomposites, and conductive polymers. The active material 16 may alsocomprise a piezoelectric material. Preferably, a piezoelectric materialis disposed on strips of a flexible metal sheet. The strips can beunimorph or bimorph. Preferably, the strips are bimorph, becausebimorphs generally exhibit more displacement than unimorphs.

Employing the piezoelectric material will likely need an electricalsignal to produce a curved shape. Upon discontinuation of the activationsignal, the activation material to straighten.

Active materials also include, but are not limited to, shape memorymaterial such as magnetic materials and magnetorheological elastomers.

Suitable magnetic materials include, but are not intended to be limitedto, soft or hard magnets; hematite; magnetite; magnetic material basedon iron, nickel, and cobalt, alloys of the foregoing, or combinationscomprising at least one of the foregoing, and the like. Alloys of iron,nickel and/or cobalt, can comprise aluminum, silicon, cobalt, nickel,vanadium, molybdenum, chromium, tungsten, manganese and/or copper.Suitable MR elastomer materials have previously been described.

The airflow control devices 10, 200, 300, 400 and methods of the presentdisclosure are able to adjust features such as shape, dimension,stiffness, location, combinations thereof, and the like by changing theat least one attribute of active material to match the needs ofdifferent driving conditions. Changes in at least one attribute ofactive material include shape, dimension, stiffness, combinationsthereof and the like. Utilizing active materials to effect these changesprovide a device 10, 200, 300, 400 of increased simplicity androbustness, while reducing the number of failure modes, device volumeand energy requirements for activation due to higher energy densities.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about”. Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe following specification and attached claims are approximations thatmay vary depending upon the desired properties sought to be obtained bythe present disclosure. At the very least, and not as an attempt tolimit the application of the doctrine of equivalents to the scope of theclaims, each numerical parameter should at least be construed in lightof the number of reported significant digits and by applying ordinaryrounding techniques.

While the invention has been described with reference to an exemplaryembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to a particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method of controlling air flow about a vehicle comprising: positioning an airflow controlling device on a surface of the vehicle, the airflow controlling device comprising a body having at least one surface, and an active material in operative communication with the at least one surface, the active material being operative to change at least one attribute of the active material in response to an activation signal; selectively introducing the activation signal upon meeting and/or exceeding a predetermined vehicle condition; and changing the at least one attribute of the active material and changing the airflow flowing about the air flow control device.
 2. The method of claim 1, further comprising: discontinuing the activation signal, wherein discontinuing the activation signal reverts the change in at least one attribute of the active material.
 3. The method of claim 1, further comprising: maintaining the change in at least one attribute of the active material upon discontinuation of the activation signal.
 4. The method of claim 1, wherein the active material comprises a helical spring shape upon discontinuation of the activation signal and a substantially straightened shape in response to the activation signal. 